1. Field of the Invention
This invention relates to a mouth-sealing structure in a cylindrical alkaline battery.
2. Description of the Prior Art
The cylindrical alkaline battery such as, for example, an alkaline dry cell uses a highly concentrated aqueous caustic alkali solution as an electrolyte. If this battery has a gap, very small as it is, therefore, it tends to suffer leakage of the electrolyte due to the so-called creeping, namely the exudation through the gap. The alkaline dry cell, accordingly, is provided with a mouth-sealing structure which is highly capable of tightly sealing the shell thereof.
In a device which uses a plurality of batteries arranged in series, for example, if the device is operated in such a state that one of the batteries is connected with the direction of polarity thereof reversed to the remaining batteries, the reversely connected battery will possibly burst when it is charged by the other batteries and caused to undergo internally a strong gas-generating reaction and, consequently, the internal pressure thereof is suffered to increase past the durability inherently owned by the mouth-sealing structure capable of sealing the shell of the battery with prominent tightness. The device, therefore, must be prevented from this accident.
For the purpose of solving this problem, mouth-sealing structures of varying types provided with an explosion-proof mechanism have been heretofore proposed for use in alkaline dry cells (as published in JP-A-59-98,452, for example).
A typical mouth-sealing structure will be specifically described below with reference to drawings.
FIG. 4 is a halved cross section of a conventional alkaline dry cell.
In a cell case 1, a positive electrode agent 2 formed of manganese dioxide and graphite and shaped cylindrically is inserted. The cylinder of this agent 2 is packed therein with an alkaline electrolyte formed mainly of potassium hydroxide and a negative electrode gel substance 3 having a gelling material and a zinc allow powder as main components thereof through the medium of a separator 4. The alkaline dry cell is further provided with a negative electrode collector 5 and a resinous gasket 6 adapted to block the opening part of the cell case 1 and possessed of a thin-wall part (an annular thin-wall part as depicted in the diagram) 7 which breaks under the pressure of gas. A negative electrode terminal plate 9 concurrently serving as a negative electrode terminal and containing a gas discharge hole 8 is mounted on the resinous gasket 6 as welded to the head part of the negative electrode collector 5 and inserted into the opening part of the cell case 1 so that the cell case 1 may be tightly sealed by folding the opening part inward. The outer lateral face of the cell case 1 and the continuing outer face of the sealed part of the opening part of the cell case 1 which has been folded inward are covered with a facing label 10 which is a thermally shrinkable insulating facing member. A positive electrode terminal 11 is disposed contiguously to the bottom face of the cell case 1.
The alkaline dry cell constructed as described above is prevented from the accidental burst mentioned above because the thin-wall part 7 of the resinous gasket 6 fractures as a safety valve when the pressure in the cell case 1 is raised past a prescribed level by the gas generated inside the cell and the gas in the cell is released through the fracture and discharged from the cell via the gas discharge hole 8 in the negative electrode terminal plate 9, with the result that the internal pressure of the cell case 1 will be lowered.
In a device which uses a plurality of dry cells each constructed as described above and together arranged in series, for example, if this device is operated in such a state that part of the batteries are erroneously connected with the direction of polarity thereof reversed to the remaining batteries, the erroneously connected cells will be charged with the other cells.
FIG. 5 illustrates the arrangement of four serially connected alkaline dry cells of the conventional construction, in which one of the four cells is connected with the direction of polarity thereof reversed to the remaining cells. The positive electrode terminal face of the reversely connected cell contacts the positive electrode terminal face of the adjoining cell and the negative electrode terminal face of the reversely connected cells contacts the negative electrode terminal face of the adjoining cell. In this case, the reversely connected cell is charged by the other cells and caused to undergo a strong gas-generating reaction. If the internal pressure of the cell case is consequently increased past a prescribed level, the annular thin-wall part of the resinous gasket as an explosion-proof mechanism for preventing the cell from the burst will fracture and the gas in the cell case will be discharged from the cell via the gas discharge hole in the negative terminal plate.
The actuation of the explosion-proof mechanism in response to an abnormal rise of the internal pressure of the cell indeed prevents the cell from the burst. It, however, has the possibility that the emanating gas will entrain the electrolyte and impel it to leak through and spout from the cell.
The electrolyte which is used in the alkaline dry cell such as, for example, a cylindrical alkaline cell is a highly concentrated aqueous caustic alkali solution. For the purpose of preventing the electrolyte from doing harm to the device in use when the explosion-proof mechanism is actuated, therefore, the alkaline dry cell is required to be so constructed that the electrolyte, even when the gas emanates through the gas discharge hole in the negative terminal plate, may neither leak nor scatter widely.
In the dry cell which is faced with such a thermally shrinkable member as mentioned above, the shrinking outer face of the facing label covering the terminal face side of the opening part of the cell case is possibly caused to peel, tear, or fracture by the friction or drop during the transportation of the cell or the insertion of the cell into the device or the extraction of the cell therefrom. Further, since the opening part of the cell case concurrently serving as the positive electrode terminal and the negative electrode terminal which approximate closely to each other are made of metallic materials, the positive and the negative electrode have the possibility of forming a short-circuit through the medium of the leading end part of a coil spring terminal on the device side while the cell is being loaded and causing the cell to gather heat and leak the electrolyte. Thus, this dry cell is required to prevent this trouble.